Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g., red, green and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Pat. Nos. 6,016,038 and 6,211,626.
Typically, an LED-based lighting unit or LED load that includes multiple LED-based light sources, such as a string of LEDs connected in series, is driven by a power converter, which receives voltage and current from mains power supply. There is a variety of power converters that have integrated power factor correction (“PFC”), particularly in connection with fluorescent ballasts. Generally, power converters may be divided into two groups. The first group includes power converters that feed back part of inverted power to the rectified mains power supply to shape the mains input current. This is accomplished based on feed back current and/or voltage. The second group includes power converters having relatively straightforward integration, in which a boost or buck-boost inverter is combined with an output stage inverter. The output stage may be a resonant type or a buck derived converter.
With respect to the power converters in the second group, duty cycle of the rectified input voltage is modulated only to control output current. Such power converters only provide coverage of narrow load ranges. Also, soft switching of a boost inverter is able to occur only in parts of the operational range, or not at all.
Thus, there is a need in the art for a power converter having a half-bridge inverter functioning as an integrated mains rectifier, boost inverter and output stage inverter, and providing power factor correction with respect to a solid state lighting load, and a method of operating the same.